What’s Up with Prominent Sun?

On Friday, 12 March 2004, the Sun ejected a spectacular ‘eruptive prominence’ into the heliosphere. SOHO, the ESA/NASA solar watchdog observatory, faithfully recorded the event.

March prominence erupts on Sun.Credit:SOHO

This ‘eruptive prominence’ is a mass of relatively cool plasma, or ionized gas. We say ‘relatively’ cool, because the plasma observed by the Extreme-ultraviolet Imaging Telescope (EIT) on board SOHO was only about 80, 000 degrees Celsius, compared to the plasma at one or two million degrees Celsius surrounding it in the Sun’s tenuous outer atmosphere, or ‘corona’.

At the time of this snapshot, the eruptive prominence seen at top right was over 700 000 kilometers across – over fifty times Earth’s diameter – and was moving at a speed of over 75 000 kilometers per hour.

Eruptive prominences of this size are associated with coronal mass ejections (CMEs), and the combination of CMEs and prominences can affect Earth’s magnetosphere when directed toward our planet. In this case, the eruptive prominence and associated CME were directed away from Earth. SOHO is a mission of international co-operation between ESA and NASA, launched in December 1995.

Every day SOHO sends thrilling images from which research scientists learn about the Sun’s nature and behavior. Experts around the world use SOHO images and data to help them predict ‘space weather’ events affecting our planet and even Mars.

During what are considered the most intense outbreaks, called X-class solar flares, the counts of bombarding charged particles reaching the Martian surface may suddenly rise a thousand-fold. The martian radiation environment experiment on NASA’s 2001 Mars Odyssey orbiter has collected data continuously from the start of the Odyssey mapping mission in March 2002 until late November, when the large amount of solar activity saturated the instruments. Validation of radiation models is a crucial step in predicting radiation-related health risks for crews of future missions.

Largest Flare Ever

Physicists in New Zealand have shown that last November’s record-breaking solar explosion was much larger than previously estimated, thanks to innovative research using the upper atmosphere as a gigantic x-ray detector. Their findings have been accepted for 17 March publication in Geophysical Research Letters, published by the American Geophysical Union.

Solar flares issue strong electromagnetic bursts.Credit:SOHO

On 4 November 2003, the largest solar flare ever recorded exploded from the Sun’s surface, sending an intense burst of radiation streaming towards the Earth. Before the storm peaked, x-rays overloaded the detectors on the Geostationary Operational Environmental Satellites (GOES), forcing scientists to estimate the flare’s size.

Taking a different route, researchers from the University of Otago used radio wave-based measurements of the x-rays’ effects on the Earth’s upper atmosphere to revise the flare’s size from a merely huge X28 to a “whopping” X45, say researchers Neil Thomson, Craig Rodger, and Richard Dowden. X-class flares are major events that can trigger radio blackouts around the world and long-lasting radiation storms in the upper atmosphere that can damage or destroy satellites. The biggest previous solar flares on record were rated X20, on 2 April 2001 and 16 August 1989.

“This makes it more than twice as large as any previously recorded flare, and if the accompanying particle and magnetic storm had been aimed at the Earth, the damage to some satellites and electrical networks could have been considerable,” says Thomson. Their calculations show that the flare’s x-ray radiation bombarding the atmosphere was equivalent to that of 5,000 Suns, though none of it reached the Earth’s surface, the researchers say.

Spectacular science from the solar observatory, or SOHO, gives the most spectacular view of solar events. SOHO is located 1.5 million kilometers (one million miles) from Earth. It orbits around the First Lagrangian point, where the combined gravity of the Earth and the sun keep SOHO in an orbit locked to the sun-Earth line.Credit:SOHO

The belt of high-energy electrons that normally cradles Earth from afar was greatly enhanced and pushed unusually close to our atmosphere during the violent solar activity. How the Earth’s radiation belts get so energized and distorted is still largely an unsolved mystery, despite the fact that Van Allen and co-workers discovered the radiation belts more than 45 years ago at the dawn of the space age. “Researchers have learned a great deal about electron acceleration in the belts in recent years,” said Xinlin Li, a professor and researcher at Colorado’s Laboratory for Atmospheric and Space Physics, LASP. “We are able to understand and forecast more normal changes in the radiation belts using our present theoretical knowledge, but extreme events ..are very hard to predict.”

At the time of the flare, the researchers were probing the ionosphere with radio waves as part of a long-term research program. Their new measurement comes from observations of the indirect effects of the increased x-ray radiation on very low frequency (VLF) radio transmissions across the Pacific Ocean from Washington State, North Dakota, and Hawaii to their receivers in Dunedin, New Zealand.

“Increases in x-rays enhance the ionosphere, causing its lowest region to decrease in altitude, which in turn affects the phase of VLF transmissions. Our previous research shows that these phase shifts are proportional to the number of kilometers [miles] by which the ionosphere is lowered,” they say. As the lowering is known to relate directly to the amount of x-ray radiation present, the team could make a new measurement of the flare’s size, they say.

“We were at the right place, at the right time with the right knowledge–which was based on nearly 15 years of work by staff and students in the Physics Department’s Space Physics Group.” The research would not have been possible, they added, without data provided by the U.S. National Oceanic and Atmospheric Administration (NOAA) Space Environment Center, which came up with the initial X28 estimate.

“We used their solar measurements to calibrate the response of the atmosphere to x-rays, so when this event overloaded the satellite detectors, we were in a unique position to make this measurement. Given that any future flares are unlikely to be large enough to overload the ionosphere, we believe that our new method has great advantages in determining their size in the event of satellite detector overloads,” they say.